The present invention relates to an image processing apparatus, an image processing method, and an image display device.
Recently, there is a widespread use of an image display device, such as a liquid crystal display device, comprising a light source and a light modulation device which modulates a light intensity from the light source. However, in the prior art image display device, the light modulation device does not have ideal modulation characteristics, and therefore, especially when black is displayed, a light leakage from the light modulation device causes reduction in contrast. Further, since the light source emits light also when black is displayed, it is difficult to reduce power consumption.
In order to solve the above problem, according to an input image, there has been proposed to perform luminance modulation of light sources of a plurality of colors corresponding to, for example, three primary colors in combination with conversion of gradation of each pixel of the input image, that is, gamma conversion.
For example, there has been known a liquid crystal display device in which the maximum and minimum values of each of red, green and blue luminance levels are detected from the input image, amplification is performed so that the maximum amplitude (a difference between the maximum value and the minimum value) of the input image is equivalent to a dynamic range width of the liquid crystal device, and the light source luminance is set based on the maximum value of the luminance level of each color (for example, see, JP-A 2007-233012 (KOKAI), JP-A 2007-72115 (KOKAI)). In the above mentioned liquid crystal display device, compared with a display device with a constant light source luminance, the contrast can be increased. Further, since the light source luminance can be reduced according to the input image, the power consumption can be reduced.
In the above prior art display device, when emitting light in a color close to an achromatic color, for example when the light source luminance is set to be lowered, the color of the displayed image is changed due to the influence of quantization error of control of the light source luminance or quantization error of gradation conversion of the input image.
In general, there has been known that human perception to luminance is approximately proportionate to the luminance to the one-third power. Namely, although the amount of variation of the luminance is the same in the low and high luminances, the variation of lightness perceived by human in the low luminance is larger than that in the high luminance. Therefore, there has been a problem that a change of color of a displayed image in the low luminance is easily perceived by human.